In the development of black-and-white silver halide photographic elements a commonly encountered problem is the accumulation of "sludge" or "dirt" in the developing composition. While the mechanisms whereby such sludge is formed are varied and complex, an important contributing factor is the presence in developing compositions of compounds such as sulfites which dissolve silver halides and form silver complexes. The silver complexes that are extracted from the photographic element into the developing composition are reduced by other components of the developing composition and converted to extremely fine particles of metallic silver which are commonly referred to in the art as "silver sludge." The formation of this silver sludge is a particularly serious problem when the photographic elements are processed in an automatic processing apparatus. Thus, for example, it is common for the sludge to attach to the walls of the developing tank and/or the rollers of an automatic processor and the particles can subsequently transfer to the photographic element. The result can manifest itself as black silver specks or silver stain and, if sufficiently severe, this can render the photographic element useless for its intended purpose. The problem can be alleviated to some extent by frequent cleaning of the processing equipment to remove accumulated silver sludge, but this adds significantly to the effort and expense of the processing operation.
The problem of reducing or avoiding the deposition of silver sludge has been a very longstanding problem in the photographic art. A wide variety of compounds has been proposed heretofore as sludge-inhibiting agents. Their effectiveness for this purpose is often insufficient. Moreover, agents used to reduce sludge formation can have unwanted side effects such as suppressing development or adversely affecting the contrast of the photographic element.
Sulfites are very commonly used in black-and-white developing compositions where they serve to extend the life of the developing composition by protecting it against aerial oxidation. While they are a major contributor to sludge formation they are not the only one. Thus, for example, other common components of developing compositions such as thiosulfates and thiocyanates also dissolve silver halide and form silver complexes. Other factors contributing to sludge formation include the throughput of sensitized material, the replenishment rate and the design of the processing apparatus. Generally speaking, most, if not all, black-and-white developing compositions suffer from the problem of sludge formation, although the degree to which it occurs varies widely depending upon both the components of the developing composition and the composition of the photographic element being processed.
U.S. Pat. No. 4,975,354 issued Dec. 4, 1990, entitled "Photographic Element Comprising An Ethyleneoxy-Substituted Amino Compound And Process Adapted To Provide High Contrast Development", by Harold I. Machonkin and Donald L. Kerr, describes silver halide photographic elements having incorporated therein a hydrazine compound which functions as a nucleator and an amino compound which functions as an incorporated booster. Such elements provide a highly desirable combination of high photographic speed, very high contrast and excellent dot quality, which renders them very useful in the field of graphic arts. Moreover, since they incorporate the booster in the photographic element, rather than using a developing solution containing a booster, they have the further advantage that they are processable in conventional, low cost, rapid-access developers.
Other patents describing silver halide photographic elements comprising a hydrazine compound which functions as a nucleator and an amino compound which functions as an incorporated booster include U.S. Pat. Nos. 4,914,003 and 5,030,547.
Nucleated high-contrast photographic elements of the type described hereinabove are particularly prone to the formation of silver sludge. While the reason for this is not clearly understood, it has been a significant factor hindering the commercial utilization of such otherwise advantageous photographic elements in the field of graphic arts.
The present invention is directed toward the objective of providing an improved developing composition, useful with a wide variety of black-and-white silver halide photographic elements, that has less tendency to sludge deposition than developing compositions utilized heretofore. It is a particular objective of the invention to provide an improved process for developing high contrast photographic elements, containing a hydrazine compound which functions as a nucleator and an amino compound which functions as an incorporated booster, utilizing the improved black-and-white developing composition of this invention.